I found red axles at a school and on my street, Atlantis pieces at a hall, and a giant box of Bionicle at a secondhand store.
I also found a near complete large Mega Bloks figure at a park.
Recently my mum found a mint condition sealed Lego games set wrapped in bubble wrap at a secondhand store (she didn't buy it )
Apart from that, my Grandma and Mum have found countless amounts of Bionicle boxes at secondhand stores. Strangely enough, they didn't buy them for me lol. Sadly now, when I'm able to go to the secondhand stores by myself, I never find any Bionicle boxes anymore.